For environmental reasons it has become desirable to reduce or eliminate the phosphate content of detergent formulations. Therefore, there is a trend towards detergent formulations containing no or reduced amounts of sodium tripolyphosphate builder material. However, a drawback of such formulations is that they may give rise to considerable scaling when applied in a washing machine. This drawback is most pronounced with detergent formulations having significant levels of alkaline ingredients such as silicates and carbonates. Such detergent formulations are usually applied in the area of industrial warewashing where they can be effectively used in the form of solid detergent briquettes. The reason for applying this type of detergent material is that it constitutes a concentrated as well as non-dusty and, therefore, relatively safe product form for the often aggressive chemicals included therein.
The accumulation of scale on table ware and on machine parts is an expensive problem causing delays and shut-downs and requiring many manhours for cleaning and removal. The term "scale" as used herein, includes deposits formed on the surface in contact with the wash liquor in the washing machine, and caused by the precipitation of metal ions from the wash liquor. There will be a considerable risk of scale formation if the wash liquor contains alkaline earth cations, such as calcium and magnesium, and anions such as carbonate, sulphate and silicate: combinations of these ions in concentrations exceeding their solubility limit form precipitates which deposit on the surface to be cleaned.
It is generally known that the accumulation of scale in aqueous systems, such as boiling water systems can be inhibited by addition to such systems of a mixture of a phosphonate and a water-soluble polymer. It is also known that treatment with such a mixture promotes the formation of a fluid sludge in the water which can be effectively conditioned and removed. U.S. Pat. No. 4,576,722 discloses a method of inhibiting the deposition of scale in a boiler water system, by adding to said boiler water a substantially water soluble polymer such as an acrylic acid polymer and a particular phosphonotricarboxylic acid.
Polymer containing formulations useful as a detergent constituent are also known in the art.
EP-A-421,664 is concerned with such detergent formulation which is in the form of granules and contains a polymer located on a water-soluble inorganic carrier material. This formulation contains at least 10% by weight of the polymer and at least 20% by weight of the carrier material, and the polymer is applied therein as a builder or anti-scaling component replacing as such the environmentally less desirable phosphate builders. This document also discloses a process for preparing the polymer containing formulation, which comprises mixing an aqueous solution of the polymer with the water-soluble inorganic carrier material, and subjecting the mixture to conditions of agitation and heat such that granules are formed.
EP-A-375,022 discloses a solid detergent composition in the form of a block of compressed granular material and a process for preparing this block-form detergent product. In this process a powder is compressed in a mould under a pressure of 3-30 kN/cm.sup.2 to form said block-form product.
It was found that effective and highly concentrated solid detergent briquettes with a density of up to 2100 kg/m.sup.3, can be produced by applying this compression process, for instance in a BEPEX briquetting machine. Such high density detergent briquettes are desirable for reducing cost of packaging, transportation and storage thereof and for minimizing the amount of packaging waste material.
In view of the foregoing, it is an object of the present invention to provide a detergent composition in the form of detergent briquettes of compressed granular material, which contains reduced levels of builder material, such as sodium tripolyphosphate, and which does not give rise to unacceptable scale formation when applied in a washing machine. It is a further object of the invention to provide a briquette-form detergent composition which is suitable for use in an industrial warewashing or fabric-washing machine.
We have now, surprisingly, found that these and other objects can be achieved by a solid detergent composition in the form of briquettes of compressed granular detergent material, comprising polycarboxylated polymer located on an inorganic watersoluble carrier material. Said briquettes were found to have optimal physical properties, such as density and compactibility, and good anti-scaling properties.
In this context, a solid detergent briquette is defined as a discretely shaped solid detergent material which may be in the form of a block, tablet or cube, of which the shape and dimensions may vary with the application envisaged, and which may have a widely varying weight in the range of 0.001-5 kg, preferably 0.004-3 kg.